1. Field of the Invention
The present invention relates to a process for producing a tubular nonwoven fabric and a tubular nonwoven fabric produced by the process. More particularly, the present invention relates to a process for producing a tubular nonwoven fabric which allows the use of various kinds of fibers, the change in the structure of the nonwoven fabric, the change in the unit weight of the nonwoven fabric, the change in the diameter of the tubular nonwoven fabric and the production stable in quality.
The tubular nonwoven fabric obtained by the process according to present invention can be used in the tubular form or in a formation wherein the tubular nonwoven fabric is folded or in a formation formed by opening the tubular nonwoven fabric by cutting, and can be used widely for filters, civil engineering materials, agricultural materials, packaging materials, wipers, etc.
Further, the present invention relates to new characteristic tubular nonwoven fabrics which are obtained by using the process according to the present invention.
2. Description of the Prior Art
JP-B-SHO 56-48624 discloses a process for producing a tubular nonwoven fabric, wherein a molten polymer extruded from an orifice is formed as fibers by a hot jet flow and a tubular nonwoven fabric is directly formed around a rotating cylinder by catching the formed fibers on the rotating cylinder. In this method, however, since the fibers still remaining soft are transferred to the rotating cylinder by the jet flow having a high speed and the fibers collide against the rotating cylinder when the tubular nonwoven fabric is formed, the tubular nonwoven fabric strongly adheres to the rotating cylinder. Therefore, it is difficult to draw the tubular nonwoven fabric from the rotating cylinder, and it may disadvantageously happen that the nonwoven fabric is elongated or broken when drawn. Moreover, in the production of a tubular nonwoven fabric high in unit weight, if many fibers are deposited on the catching surface of the rotating cylinder, they are blown away by the high velocity hot jet flow. As a result, a uniform tubular nonwoven fabric cannot be obtained. Furthermore, in the production of a tubular nonwoven fabric, the diameter of the tubular nonwoven fabric cannot be changed freely.
A tubular nonwoven fabric obtained by such a process is small in strength because it is composed of unstretched fibers, and so cannot be used for applications requiring high strengths. Further, it is poor in dimensional stability disadvantageously.
Electret tubular nonwoven fabrics excellent in electrical adsorbability, filterability and mechanical strength can be used for various uses such as bag filters, filters for cleaners, filters for copy machines, wipers, hair caps, masks, etc.
JP-B-SHO 59-124 discloses a process for producing an electret nonwoven fabric. However, when the electret nonwoven fabric obtained by this process is formed as a tubular nonwoven fabric, both ends of the nonwoven fabric must be sewn. In such a forming process, the strength of the fabric decreases at the sewn portion, and the adsorbability of the fabric decreases by the existence of the sewing threads. Moreover, for example, when it is used as a filter, the collection efficiency is insufficient.